Surgical treatment for left atrial rupture due to myxomatous mitral valve disease in three dogs: A case report

Abstract Introduction Myxomatous mitral valve degeneration (MMVD) is an acquired heart disease which sometimes result in pulmonary oedema and left atrial rupture. In previous reports, left atrial rupture has been non‐surgically controlled and its prognosis investigated. There is, however, no report concerning surgically treated left atrial rupture with mitral valvuloplasty and follow‐up results. Objectives This report aimed to develop a surgical strategy for a case of left atrial rupture caused by MMVD. Materials and methods Three dogs were presented at a private hospital for surgical treatment of MMVD. All three dogs had a previous history of left atrial rupture due to MMVD. The left atrium rapture was diagnosed from indicating that characteristics of the drained pericardial effusion consistent with blood. Mitral valvuloplasty was performed in all dogs using an extracorporeal circulation machine, and the surgical procedure was modified according to each case. In cases with severe adhesion between the pericardial and left atrial appendage, suturing of the left atrial appendage was performed strategically. Additionally, in cases with severe hypotension caused by left atrial rupture, cardiopulmonary bypass was started as soon as possible during the surgical procedure. Discussion and Conclusion Since the haemodynamics of all dogs had improved, and the owner reported no cardiac‐related clinical signs, all drugs were withdrawn 3 months after surgery. Since left atrial rupture due to MMVD can cause hypotension, cardiopulmonary bypass should be started as soon as possible during the surgical procedure to maintain the blood pressure and suturing of the left atrial appendage should be performed strategically.


INTRODUCTION
Myxomatous mitral valve degeneration (MMVD) is an acquired heart disease that commonly causes left-sided congestive heart failure (CHF) in dogs (Buchanan, 1977;Serres et al., 2007). The prevalence of MMVD increases markedly with age in small breed dogs and if the regurgitation continues to worsen, increased left atrial pressure will result in pulmonary oedema and sometimes left -atrial rupture (Buchanan, 1972;Fox, 2012;Nakamura et al., 2014;Sadanaga et al., 1990). Although left atrial rupture has been reported as a rare consequence of MMVD in dogs, left atrial rupture can cause rapid bleeding and cardiac tamponade, and in some cases sudden death (Buchanan, 1972;Fox, 2012;Nakamura et al., 2014). Sometimes, as a result of left atrial rupture, left atrial pressure may decrease and bleeding may stop. However, the underlying mitral valve disease is progressive and most patients will die of recurrent CHF or complications during medical treatment (Serres et al., 2007). In previous reports, left atrial rupture has been nonsurgically controlled and its prognosis investigated (Reineke et al., 2008).
Medical treatment can improve dog's condition temporarily. However, due to medical treatment for left atrial rupture being palliative unless the MMVD is radically cured, MMVD remains progressive with a poor prognosis. There is, however, no report concerning surgically treated left atrial rupture and follow-up results. Here we present three cases of left atrial rupture caused by MMVD, in which Mitral valvuloplasty (MVP) was performed. Depending on the site of rupture and pericardial adhesion, the surgical procedure was adjusted to cope with each specific situation. All three cases achieved long-term survival, with complete cessation of cardiac medication.

CASE DESCRIPTION
All three dogs were presented to private hospital for surgical treatment of MMVD. Abbreviations: A velocity, peak velocity of late diastolic transmitral flow; BW, body weight; E/A, the ratio of peak velocity of early diastolic transmitral flow to peak velocity of late diastolic transmitral flow; E velocity, peak velocity of early diastolic transmitral flow; E' , early diastolic wave signal as measured by Tissue Doppler imaging; FS, fractional shortening; HR, heart rate; LA/Ao, the ratio of the left atrial dimension to the aortic annulus dimension; lat, mitral annulus at the left ventricular lateral wall; LVIDd, left ventricular end-diastolic diameter; LVIDDN, left ventricular end-diastolic internal diameter normalized to body weight; sep, mitral annulus at the septal wall. Note: LVIDD was standardised by dividing LVIDD to the body weight (BW) raised to the 0.294 power (Cornell et al., 2004). LVIDDN was calculated using an allometric approach.
effusion was recognised on echocardiography. The left atrium rapture due to MMVD was diagnosed from exhibiting that characteristics of the drained pericardial effusion consistent with blood (Ht 42%, HGB 13.3 g/dl). An emergency operation to identify the haemorrhage site and control the active bleeding was performed.
Concomitantly, MVP was performed for the definitive treatment of MMVD.
Case 3 was presented for MVP due to repeated episodes of pulmonary oedema. No pericardial effusion was recognised on echocar-

Surgical procedure
For Case 1, the surgical steps were followed in the usual order (procedures 1→7) Yoshida et al., 2021)(reference to below for each procedure description). For Case 2, since the surgery was performed as an emergency operation on the day when the left atrial rupture occurred, procedure 4 had precedence over others. In addition, to maintain blood pressure, a connection to an extracorporeal circulation machine was made as soon as possible (procedures In Case 2, due to blood pressure compromise, premedication with fentanyl and midazolam was suspended.

Procedure 2: Haemodynamic monitoring
The right femoral artery and vein were cannulated to measure arterial and central venous blood pressure.

Procedure 3: Thoracotomy and approach to the left atrium
After left intercostal thoracotomy, a pericardial incision was conducted to approach the left atrium appendage. In Cases 1 and 2, pericardial effusion was visually identified by thoracotomy. In addition, blood mixed with clots was collected after the pericardiectomy. While the ruptured site of the left atrium was blocked with clotted blood in Case 1, in Case 2, there was slight yet continuous haemorrhage from the rupture (Figure 1a (Nakamura et al., 2014). On the other hand, the survival time of dogs that survived the acute phase of left atrial rupture has been extended, to some degree, through medical management (Reineke et al., 2008). Emergency surgery in cases with left atrial rupture demands swift connection to the extracorporeal circulation machine in order to maintain the blood pressure. In Case 2, the acute nature of the left atrial rupture that occurred immediately before surgery required even earlier connection to the extracorporeal circulation machine. In Case 3, concerns regarding the risk of haemorrhage and subsequent decrease in blood pressure during detachment of adhered pericardium led to the decision to prioritise the extracorporeal circulation connection. However, early extracorporeal circulation connection necessitated even earlier heparin administration, that is, immediately after the procedure began, which also increased the risk of haemorrhage. In the standard operation, heparin is usually given after thoracotomy is performed (Fox, 2012;Suzuki et al., 2020;Uechi, 2012). Third, surgical difficulty may increase if adhesion between the left atrial appendage and pericardium is present due to left atrial rupture. What makes Case 3 unique is that adhesion between the left atrial appendage and pericardium necessitated different approaches to incise and suture the left atrial appendage than those of Cases 1 and 2. The aggressive removal of the adhered pericardium might have resulted in haemorrhaging from the left atrial appendage. Therefore, instead of detachment, trimming around the adhered pericardium was performed. Also, the left atrial appendage incision and closure were conducted with the adhered pericardium at once. If the rupture and surgical sites were not consistent, purse-string suturing might have been necessary. In this report, we surgically corrected left atrial rupture cases caused by MMVD. It is hard to judge whether a surgical correction should be immediately performed at the time the atrial rupture is found. Provided the client is obtained, and immediate surgery is available, surgery is considered an effective treatment option as well. Nevertheless, in general, as the availability of surgery is limited, medical management before surgical correction is also essential.
In conclusion, this study reports the therapeutic strategy for dogs with left atrial rupture due to severe MMVD. To fundamentally treat left atrial rupture, mitral valve reconstruction and suture annuloplasty were performed under cardiopulmonary bypass. Our findings suggest that in cases with severe adhesion between the pericardial and left atrial appendage, suturing of the left atrial appendage should be performed strategically. In addition, cardiopulmonary bypass should be started as soon as possible during the procedure.

AUTHOR CONTRIBUTIONS
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